Safety metric calculation

Reliability and safety metrics can be calculated using matrix techniques from this P matrix. 

The assessment and analysis of the inherent safety performance in the hydrogen system requires sound and appropriate metrics. Several valuable proposals for inherent safety metrics (Cozzani et al. 2007, Tugnoli et al. 2007) as well as the main issues needed for such assessment are well summarized in the literature (Roller ef a/. 2001, Khan eta/. 2003). Recently, a novel consequence-based approach for inherent safety key performance indicators (KPI) assessment was proposed (Tugnoli et al. 2007). The approach bases the calculation of safety indicators on the evaluation of the expected outcomes of the hazard present in the system, by runs of specific physical consequence models. The KPI method was preferred in the current assessment framework, since, unlike other approaches, it allows easily fitting the peculiarities of the analysed systems and does not require subjective judgment. Furthermore, the KPI method was newly reviewed to describe some particular features of the hydrogen chain. In particular the assessment of transport units was added and new index aggregation rules were defined. 

In TSC, the results of FMEA should be captured and the catalog of typical hardware failures from Annex D of ISO 26262 Part 5 should be considered, in order to be sure that all potential failure modes have been dealt with. It is recommendable to use links between safety mechanisms and failure modes or to arrange them in a matrix notation (as in [11], for instance) in order to demonstrate to reviewers and assessors that all failure modes have been covered by safety mechanisms. In cases where quantitative analysis and metrics calculation is required, this demonstration has to be performed in a quantitative manner, as well, regarding the Diagnostic Coverage of each safety mechanism. This requires FMEDA or quantitative Fault Tree Analysis to be carried out. A few examples of typical technical safety mechanisms in the context of CMS could be ... 

Effective mass yield includes actual reagent masses as well as solvents. In effective mass yield, Hudlicky chose to include only nonbenign reagents. Benign reagents include water, dilute saline solutions, and ethanol. The safety of some reagents is debatable, and the subjective nature of effective mass yield calculations is a weakness in the metric. 

Markov models are a reliability and safety modeling technique that uses state diagrams. These diagrams have only two simple s)rmbols (see Figure 5-17) a circle representing a working or a failed system state and a transition arc representing a movement between states caused by a failure or a repair. Solution techniques for Markov models can directly calculate many different metrics compared to other reliability and safety evaluation techniques (Ref. 9). 

Thus, in manufacturing process the probability to fail to respect the modulus is very low. This probabiUty can be calculated a it = p. p2 Pi where pj is the failure probabiUty that barrier J faUs. Generally, the SMP are quality control operations, there are given by standards or regulations which specify the safety level associated to each barrier. The probabiUty associated to a barrier or SMP is a metric to assess the efficiency of the barrier. 

Evaluation. The design options are checked with respect to their performance. Taking the wide range of criteria in the safety, health, onomics, enviromnent and t echnology (SHEET) aspects speciflc choices are made for economic performance, sustainability and technology. With respect to economics, we calculate the capital and operational costs of a process for its time horizon. We use exergy efficiency as a sustainability metric, while a systems response time is used to define the responsiveness of the process. 

An optimized development therefore takes these metrics as criteria for optimization and considers both expected safety benefit as well as possible negative consequences. In order to test false-positive rates or calculate NNT, adequate testing methods with respect to real traffic and its variability are needed [9, 10]. 

The Occupational Safety and Health Administration used metric values to calculate the clearing times in Table 6 and Table 7. An employer may use English units to calculate clearing times instead even though the results will differ slightly. 

Hydrodealkylation of toluene is a process where toluene is converted into benzene by reaction with hydrogen, forming Diphenyl as a byproduct. This is a well known process, which has been studied in numerous publications. The reference design and flowsheet considered in this paper are taken from Seider et al. (1999), where further details can be found. The necessary steady state simulations have been performed with a commercial process simulator, from where the results have been transferred to a software developed for this work to calculate the indicator values. The steady state simulation results are also transferred to ICAS (ICAS Documentation, 2002) to determine the environmental impact factors, the sustainability metrics and the safety factors. Table 1 shows the most important indicator-values from the base case design. A detailed calculation results document can be obtained from the corresponding author. 

A common metric used to evaluate safety performance is the injury rate. An injury rate is derived from an equation that takes into consideration the number of hours worked within the school being evaluated. An injury rate is calculated by multiplying... 

C.2.1 This requirement applies to ASIL (B), C, and D of the safety goal. The definition given by the following equation shall be used when calculating the single-point fault metric ... 

All the performance metrics, except the overhead and the channel utilization, are calculated separately for the periodic and event-driven safety messages. 

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